Generally, in a polymerization reactor system, in order to measure the properties of a polymer, especially a copolymer, and control a polymerization reaction online, the properties thus measured must be analyzed.
An example of such a case is a property evaluation of a resist (composition for a resist), a type of copolymer, which is a composition for lithography used in a manufacturing process of a semiconductor element.
In recent years, in processes for manufacturing semiconductors, liquid crystal devices, and the like, rapid progress has been made in formation of a finer pattern using lithography. Examples of technology for formation of a finer pattern include a technology using shorter wave radiation on the resist upon pattern formation.
In recent years, KrF excimer laser (wavelength: 248 nm) lithographic technology has been introduced. Also, ArF excimer laser (wavelength: 193 nm) lithographic technology and EUV (wavelength: 13.5 nm) lithographic technology, which are intended to use shorter wavelengths, have been investigated.
Furthermore, for example, a so-called chemical amplification type resist has been proposed as a resist compound suitably applicable to shorten the wavelength of irradiation light and to pattern microfabrication. Such a chemical amplification type resist includes a polymer, which becomes soluble in alkali when an acid-eliminable group is dissociated by the action of an acid, and a photoacid generator. The resist composition has been further developed and improved.
An acrylic type polymer transparent to light with a wavelength of 193 nm has attracted attention as a chemical amplification resist polymer used in ArF excimer laser lithography.
As such an acrylic type polymer, copolymers for resist that are produced using, as monomers, (A) a (meth)acrylate to which an aliphatic hydrocarbon having a lactone ring is ester-bonded, (B) a (meth)acrylate to which a group dissociable by the action of an acid is ester-bonded, and (C) a (meth)acrylate to which a hydrocarbon group or an oxygen atom-containing heterocyclic group having a polar substituent is ester-bonded are disclosed (for example, refer to Patent Document 1).
Incidentally, a (meth)acrylate polymer is obtained by radical polymerization.
In a multi-component polymer produced from at least two types of monomers, the monomers have their respective copolymerization reaction rates. Thus, the copolymer composition ratio of the polymer in the early stage is different from that in the later polymerization stage. Namely, the resulting polymer has a composition distribution.
When a polymer has variations in the composition ratio of monomer units, the solubility of the copolymer tends to be less in a solvent. Thus, the preparation of a resist composition may be affected. For example, preparation of a resist composition takes a long time to dissolve the copolymer in a solvent, and causes an increase in the number of production steps due to generation of an insoluble substance. Also, the obtained resist composition tends to have insufficient sensitivity.
In addition, generally in a multi-component polymer, a chain order varies depending on the polymerization reaction rate between monomers. Since a copolymer having a large number of chains in which the monomer units are arranged successively tends to deteriorate resist performance, a copolymer with a reduced number of chains in which the monomer units are arranged successively has been desired.
On the other hand, for example, a method for obtaining a polymer having a narrow copolymer composition distribution has been disclosed that makes a difference between the feed rate of a monomer having a relatively higher polymerization rate to a monomer having a lower polymerization rate in the front end of the process and that in the back end of the process to obtain a resist having high resolution (for example, refer to Patent Documents 2 and 3).
In a copolymer for resist produced by a method of Patent Documents 2 and 3, a bias of monomer units incorporated into the copolymer is reduced and a proportion of the chain in which monomer units are arranged successively is smaller than in a method of simultaneously adding the above-described monomer, a polymerization solvent, a polymerization initiator, and a chain transfer agent in some cases into a polymerization apparatus, and therefore such a copolymer is superior in solubility in resist solvent and flatness of resist pattern sidewall.
However, with the methods described in the above Patent Documents 2 and 3, improvement in the solubility of a copolymer for lithography or the sensitivity of a resist composition may be insufficient.
With progress of formation of a finer pattern using lithography, there is a need for a copolymer for resist that is: lower in a proportion of chains in which monomer units (monomers of the same type) are arranged successively and/or smaller in variation in the composition ratio of the monomer units; industrially higher in resist sensitivity and/or in resolution; and superior in solubility in the resist solvent, than a conventional copolymer.
In general, the chain structure of a copolymer is determined from intensity of signals unique to factors, such as signals found in signals obtained by: a spectrochemical analysis method such as a nuclear magnetic resonance (NMR) method and an infrared absorption (IR) method; a separating analysis method such as a pyrolysis gas chromatography (PyGC) method; or a mass spectroscopic analysis (MS) method (for example, refer to Non-Patent Document 1).
However, there may be a case in which the signals obtained from the measurement result cannot clearly be separated, due to the increased number of constitutional units in a copolymer, due to overlap between characterizing signals of factors even if the number of constitutional units is small, or the like. In addition, precision may be low due to: time-consuming analysis of data obtained by the measurement; and likelihood of quantitative values obtained from the result of analysis.
Therefore, the result obtained may not be used effectively in quality management of copolymers and the like.
Meanwhile, in recent years, analysis called multivariate analysis or chemometrics that uses a method aimed at maximization of chemical information acquired from chemical data such as spectra and chromatograms obtained by various measurements by applying mathematical or statistical technique has been practiced. Examples of such analysis include a method of identifying a polymer material from a near-infrared spectrum and a method of measuring density (for example, refer to Patent Documents 4 and 5).